The present invention relates generally to apparatus for evaluating heat exchange systems. More specifically, the present invention relates to apparatus for evaluating the heat transfer efficiency of a heat exchange wall and/or the overall cleanliness thereof.
Maintaining an acceptable heat transfer efficiency of a heat exchange system is indeed important to the successful operation of the system. For example, it is known that a decrease in heat exchange system efficiency typically means an increase in operating costs.
Heat exchangers are characteristically used in industrial processes of all types for the removal of excess, unwanted or undesirable heat. The heat exchanger normally removes the heat by passing a relatively cold fluid through a heat exchange area which is adjacent to and in thermally conductive contact with a heat exchange area containing the fluid from which the heat is to be removed. These areas are typically separated by a wall of thermally conductive material, usually comprising a metal, which conducts heat from one side thereof to the other.
It has been observed by the present inventor that the overall cleanliness of the wall of thermally conductive material separating the heat exchange areas indeed affects the heat transfer efficiency of the wall. For example, the effect of surface fouling on the heat transfer efficiency of the wall can be observed in a petroleum refinery. The relatively hot fluids to be cooled are likely to be hydrocarbons, and if fouling is not a problem, the hot side of the wall will probably retain good heat transfer characteristics. However, the cold side of the conductive material is likely to be contacted with aerated, corrosive, and deposit-forming cooling fluid which will foul the wall surface. Also, fouling of the wall surface results from dissolved scale-forming substances such as calcium carbonate and calcium sulfate. It should be appreciated that such fouling, which affects the overall cleanliness of the wall, can significantly reduce the heat transfer efficiency of the wall, and therefore, the entire heat exchange system.
Therefore, it can be seen that it is desirable to have a method for determining the effects of fouling (overall cleanliness) on the heat transfer efficiency of a heat exchange wall. That is, if such determinations and/or measurements are performed, the heat exchange efficiency of the wall could be monitored or evaluated and optimized.
Accordingly, the present invention provides apparatus which facilitates determination of the heat transfer efficiency of a heat exchange wall having at least one heat transfer surface exposed to heat exchange fluid. The apparatus of the present invention comprises means for imposing a heat load on a first heat transfer surface of the wall and means for determining the rate of dissipation of the heat load across the wall and into the heat exchange fluid.
According to a first preferred embodiment of the present invention, the heat load is imposed upon the heat transfer surface by a heating element located adjacent to or in contact with the surface. Located closely adjacent to the heating element is a first temperature sensor which is connected to a thermometer for measuring the temperature at the first heat transfer surface. Insulation is provided about the heating element to minimize heat loss to the ambient. Second temperature sensing means are located adjacent a second heat transfer surface of the heat exchange wall which second heat transfer surface is exposed to heat exchange fluid. The second temperature means is also connected to a thermometer for measuring the temperature of the heat exchange fluid. Timer means are provided for timing the dissipation of the imposed heat load. From this timed dissipation of the heat load imposed on the first heat transfer surface, the heat transfer efficiency or cleanliness of the wall can be evaluated and/or monitored.
According to another preferred embodiment of the present invention, the temperatures sensed by the temperature sensor are fed directly into an automatic device which gives a read-out of a heat transfer efficiency or wall cleanliness value. Also, the heater is automatically controlled so that operation of the apparatus can be completely automatic.
Accordingly, it is an object of the present invention to provide apparatus which, by relatively simple means, facilitates determination of the heat transfer efficiency and/or the overall cleanliness of a heat exchange wall.
Another object of the present invention resides in apparatus for evaluating the heat transfer efficiency of a heat exchange wall which apparatus is very simple in construction and relatively inexpensive.
Yet another object of the present invention relates to apparatus which automatically provides a read-out value of the heat transfer efficiency of a heat exchange wall.